1. Field of the Invention
This invention relates to a lens barrel rotation detection apparatus and a lens barrel rotation type image pickup apparatus wherein a rotational state of a lens barrel to which a lens for image pickup apparatus is attached and which is rotated in a horizontal direction or a vertical direction by driving force of a driving source is detected.
2. Description of the Related Art
For example, a video camera for a videoconference and a security video camera are known as lens barrel rotation type image pickup apparatus wherein the lens barrel rotates. Video cameras of the type mentioned are configured from applications thereof such that the lens barrel can rotate in a horizontal direction (hereinafter referred to as panning direction) and a vertical direction (hereinafter referred to as tilting direction). In particular, the lens barrel is mounted for rotation in a panning direction and a tilting direction toward an image pickup subject so that the image pickup subject can be captured at the center of a picked up image. Further, a rotational state of the lens barrel, that is, presence or absence of rotation of the lens barrel and a limit position of a range of rotation, can be detected.
In related art, as rotational driving mechanisms for a panning direction or a tilting direction, those of the direct type and those of the speed reduction type are known. In a rotational driving mechanism of the direct type, a driving motor, that is, a driving source, which exerts rotational driving force, is connected directly to a pedestal which is rotatable together with the lens barrel supported thereon without including a speed reduction mechanism formed from gear wheels or the like. On the other hand, in a rotational driving mechanism of the speed reduction type, a plurality of plain gear wheels and so forth are combined to transmit driving force of the driving motor while reducing the speed of rotation of the driving motor so that the lens barrel can be driven to rotate even if the lens barrel is large and heavy. Further, of whichever one of the direct type and the speed reduction type the rotational driving mechanism is, it includes a lens barrel rotation detection apparatus for detecting a rotational state of the lens barrel, that is, presence or absence of rotation of the lens barrel and a limit position of a range of rotation.
Incidentally, an image pickup apparatus having a zoom function includes a zoom position detection apparatus for detecting a limit position of a zoom range. The zoom position detection apparatus can detect a moved position of the lens when the focal distance of the lens is varied by electric driving operation. To this end, the zoom position detection apparatus includes a comb-shaped rotational member for rotating together with rotation of a focus ring or a zoom motor and two photo-couplers for detecting the rotational state of the rotational member. The moved state of the lens, that is, presence or absence of rotation of the focus ring or the zoom motor and a limit position of the range of rotation, are detected from an output pattern of the two photo-couplers which varies depending upon whether light beams emitted from light emitting members of the photo-couplers are intercepted by or are transmitted between the teeth of the comb-shaped rotational member, that is, depending upon whether the light receiving member of each of the photo-couplers is placed into a no-light receiving state or a light receiving state. A zoom position detection apparatus of the type described is disclosed, for example, in Japanese Patent Laid-Open No. Hei 5-11163 (hereinafter referred to as Patent Document 1) or Japanese Patent Laid-Open No. 2001-324664 (hereinafter referred to as Patent Document 2).
Although both of Patent Document 1 and Patent Document 2 are directed not to a lens barrel rotation detection apparatus but to a zoom position detection apparatus, since the apparatus of both documents can detect presence or absence of rotation of a focus ring or a zoom motor or a limit position of a range of rotation, it is considered possible to apply the apparatus to a lens barrel rotation detection apparatus if a similar rotational member and similar photo-couplers are used. For example, if a comb-shaped rotational member which rotates together with rotation of a lens barrel is used and the rotational state of the rotational member, that is, presence or absence of rotation of the rotational member and a limit position of a range of the rotation, are detected by two photo-couplers, then rotation of the lens barrel can be detected.